kukun kun has been uploading tons of rare old Japanese gaming TV shows and personal game recordings. This recently-uploaded episode of Famitsu's “Game Catalogue II” program covers E3 1996. The coverage of Sega's booth (starting around 9 minutes) shows some footage of the extremely ill-fated Sonic X-Treme. It looks pretty but there's not much to it. We see Sonic running around a flat room with a spiral of rings in the center.
Immediately after we get a look at the first level of Sonic 3D Blast for Genesis. It seems to just be called “Sonic Blast” at this point. A demo unit for the GameGear version seems to be sandwiched between two units for the Genesis game.
The channel has tons of interesting rarities. Here's a playlist of vintage gameplay from the Sega Game Library, a service somewhat similar to the Sega Channel, much of which has been lost to time. There's also footage from Nintendo's Satellaview service, and plenty more gaming-related TV shows. Give it a look!